1. Technical Field
This invention relates generally to linear printheads for document imaging apparatus such as printers, copiers, facsimiles, and the like; more particularly, this invention relates to the adjustment of the pressure profile seen by the media at the moment imaging is occurring.
2. Background Art
Document imaging apparatus often includes a printhead consisting of a linear array of print elements that extend across a substantial portion, if not all, of the width of the image to be produced. In many cases the media to be printed on is held against the print elements by a platen roller. There are many factors, such as flexing and thermal distortion of the printhead, the platen roller, and any mounting members, that can cause an undesired pressure variation across the width of the image to be produced. This undesired pressure variation can directly impact image quality. In addition, the pressure profile along the line of print elements can change during the operation of the document imaging apparatus. One example of this is the change in the printhead temperatures in a thermal printer when printing dark vs. light images.
One approach taken in the prior art such as described in U.S. Pat. No. 5,735,617 is to deform the printhead into a desired shape with screws pushing the head away or pulling the head towards another mounting member; the goal presumably being to achieve a desired pressure profile once all the members have flexed and thermally distorted. This method does not allow for adjustments during the operation of the apparatus. Nor does it allow for variations in physical properties of the media, such as thickness and stiffness. Such variations greatly affect the overall force profile.
It should be noted that there exists much prior art describing different ways to adjust the total load applied to the printhead (e.g., U.S. Pat. No. 5,448,281.) Although the present invention also achieves this end, the adjusting of the load distribution along the line of print elements during the operation of the apparatus is made possible as well.
It is an object of the present invention to provide a device for loading a printhead that allows adjustment of the pressure profile along the print line prior to and during operation of the apparatus.
According to a feature of the present invention, a printhead loading or load applying device includes a plurality of members that can each apply an individually adjustable load to a precise point along the length of the printhead. The location of the point of the applied load is also adjustable for each of these members. Thus, the pressure profile along the print line and the total applied load can be controlled by changing the magnitude and/or location of any (or all) of the loads applied to the printhead.
In accordance with a first aspect of the invention, there is provided a method of recording on an image recording medium using an imaging member in pressure engagement with the medium, the method comprising sensing an operating parameter of a recording operation; and in response to said sensing adjusting a pressure profile operating on the medium by the imaging member.
In accordance with a second aspect of the invention, there is provided an apparatus for recording information on an image recording medium, the apparatus comprising a support for supporting an image recording medium during movement of the image recording medium in a first direction; an imaging member in pressure engagement with the recording medium; a sensor for sensing an operating parameter of a recording operation and generating a first signal relative to sensing of the parameter; a controller responsive to the first signal from the sensor for providing an output signal for adjusting a pressure profile for recording in response to the first signal; and a pressure applying member movable in a direction transverse to the first direction and cooperating with the imaging member to adjust the recording pressure profile of the imaging member upon the recording medium.
In accordance with a third aspect of the invention, there is provided a method of recording on an image recording medium using an imaging member in pressure engagement with the medium, the method comprising sensing an operating parameter of a recording operation upon the recording medium, the recording medium being movable in a first direction; and adjusting the position of a pressure applying member in a direction transverse to the direction of movement of the recording medium to adjust a pressure profile on the recording medium.